Method of controlling the length of metal chips

ABSTRACT

A method is disclosed for controlling the length of chips removed from a workpiece that is being machined. A path is etched into the surface of the workpiece by a laser beam and defines a pattern of chip break points. The material is cut away from the workpiece along a second path which periodically intersects with the first path. At the intersection point a chip will break away from the workpiece. By controlling the distance between intersection points, the present invention allows one to control the length of the chips formed during machining.

This is a continuation of copending application Ser. No. 07/650,466filed on Feb. 14, 1991, now U.S. Pat. No. 5,300,593.

BACKGROUND OF THE INVENTION

This application relates to a method of machining a part, wherein thelength of metal chips removed from the part can be controlled. Moreparticularly, the present invention relates to a method of ensuring thatthe length of the chips is within a predetermined range.

Machining operations as known in the prior art have problems with chipsremoved from a workpiece. These chips cause problems if they are overlylong, or too short. The chips can clog cutting machinery, which coulddamage the machinery or cause downtime. Further, long chips can scorefinished surfaces. Lastly, the chips may be somewhat dangerous tooperators.

In response to this problem, attempts have been made to control chiplength. One known solution is to periodically apply a high pressurewater jet to the chip when it reaches a desired length. This approachhas proved unsatisfactory since it does not provide adequate accuracy inchip length.

Another known prior art solution involves the use of a mechanicalscribe, which scribes a chip break line into the part. As the part ismachined, chips will form from the part until it reaches the chip breakline, at which time the chips break off. Mechanical scribes have beenunsuccessful for several reasons. First, they are inaccurate in thedepth of the chip break line that they cut in the part. Also, the metalon metal contact of the scribe on the part results in undesirable wear.Further, the scribe mechanisms are complicated, too slow, and typicallyare not adaptable to machine different sized workpieces.

In one disclosed method, a laser beam is moved relative to a workpieceto etch the chip break line into the workpiece. In a disclosedembodiment, the workpiece is rotated while the laser beam is movedradially over the workpiece surface. The laser is preferably mounted ona robot arm which moves about the workpiece. In this way a pattern isformed in the workpiece. By controlling the speed of rotation, the speedof radial movement of the laser and the intensity of the laser, thedepth of the break line can be controlled. Further, the size or width ofthe break line can also be controlled by controlling the various laservariables.

In one disclosed embodiment, a torque convertor housing end plate ismachined using the method according to the present invention. It shouldbe understood, however, that the method of the present invention willextend to machining of any known part and particularly including tubularmembers, or other non-planar parts.

These and other objects and features of the present invention can bebest understood from the following specification and drawings, of whichthe following is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a workpiece to be machined by the methodof the present invention.

FIG. 2 is a largely schematic view of an apparatus for performing themethod of the present invention.

FIG. 3 is a cross-sectional view of a portion of the workpiece beingmachined.

FIG. 4 is a schematic view showing a portion of the workpiece beingmachined by the present invention.

FIG. 5 is a view similar to FIG. 4 schematically showing machining ofthe workpiece.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A method of machining a workpiece or part 20 will be disclosed. Part 20is illustrated in FIG. 1 as a torque convertor end plate housing havingan inner ring 22 and an outer periphery 24. Material 26 between ring 22and outer periphery 24 is to be removed by a rim cutting machiningprocess. Essentially, a cutting element removes material from the planeof material 26 to define a finished surface. In such machiningoperations, chips of machined material are typically formed. An etchedchip break pattern 28 is formed and controls the length of those chips.Although a particular generally planar part 20 is illustrated, it shouldbe understood that the teachings of this invention extend to the removalof any type of material from any type of workpiece including tubular orother non-planar workpieces. The teachings of this invention allow anoperator to control chip length in any machining operation, includingturning, boring, chamfering or other operations. The disclosed part 20is formed of a relatively soft metal, and the teachings of thisinvention are particularly useful in combination with machining of softmetal workpieces, which typically have problems with chip length.

FIG. 2 schematically shows etching system 30 including laser 32 whichincludes robot arm 34 moving laser tip 36 about part 20. Part 20 isrotated on rotary plate 38. Robot arm 34 moves laser tip 36 radially onpart 22, such that etched pattern 28 is formed. By controlling the speedof rotation of rotary plate 38, the speed of movement of laser tip 36,and the intensity of the laser beam from laser tip 26, the pattern anddepth of cut of break line pattern 28 is controlled.

Once pattern 28 has been etched into part 20, a machining operationtakes place. As a known material removing or cutting element crossesmaterial 26, chips will be formed until the chip reaches a break lineformed by a portion of pattern 28. The break line causes the chip tobreak off. The pattern is selected such that the majority of the chipsformed will fall within a desired range of lengths. Some of the chipsformed may be relatively short, while others may be relatively long. Itmay not be necessary to completely control chip lengths, and thus arange may be acceptable. The present invention allows an operator todetermine a desired range of chip lengths and have the majority of thechips fall within that range. If it is important to ensure that thatrange is extremely small, the pattern may be determined, in combinationwith the movement of the cutting element, to result in chips within thedesired range of lengths. The details of determining the desired patternis within the skill of a worker in the art.

FIG. 3 shows a portion of part 20. Adjacent chip break lines 41 and 42,which form a portion of pattern 28 are formed in material 26. Cuttingelement 43 cuts across material 26 and begins to form chip 44. Cuttingchip 44 begins at chip break line 42 with cutting element 43 moving tothe left as shown in this figure. Chip 44 is formed through distance 45until cutting element 43 reaches chip break line 41. At that time, chip44 breaks away. Chip 44 is approximately of a length defined by thedistance between lines 41 and 42, which is controlled to result in chipsof the desired length. The depth of chip break lines 41 and 42 isapproximately equal to a the cuting depth defined by line 46. The depthof the etched chip break line is preferably approximately equal to thecutting depth. If a finished surface is being machined, the depth of thebreak line should be less than, or equal to, the cutting depth.

FIG. 4 is a partial view of workpiece 20 having pattern 28 etched by alaser beam. Pattern 28 includes break line portions 41 and 42 spacedfrom each other by a predetermined distance. This distance will roughlycorrespond to the length of chips formed as the material between thebreak lines is removed. Obviously this distance changes across thethickness of workpiece 20, and this change results in the range of chiplengths.

FIG. 5 schematically illustrates cutting element 43 removing material 26from workpiece 20. In the discussed embodiment, workpiece 20 is rotatedand cutting element 43 is moved radially along the surface removingmaterial 26. Chips are formed beginning from a particular break line,such as break line 42, until the chip crosses break line 41. At thatpoint, the chip breaks away from workpiece 20. By controlling thedistance between adjacent break lines 41 and 42 the size of the chipsformed can be controlled.

In a sense, the etching could be said to be creating a first chip breakpath, and the cutting could be said to be directed along a second pathwhich periodically intersects the first path. The intersection pointsbetween the paths define break points for the chips. Thus, bycontrolling the distance between these intersection points, either bycontrolling the pattern of the etched first path, or the movement of thecutting element, one can control the length of the chips removed fromthe material.

In a most preferred embodiment of the present invention, the laser is aCO₂ laser. A laser available from Mazik, a Japanese company may be used.Other types and brands of lasers may be selected depending on thematerial being machined. Although a particular system for etching theworkpiece has been disclosed, it should be understood that the teachingsof this invention extend beyond the use of a particular laser, or eventhe use of lasers generally. The broad teachings of this inventionextend to any fluent beam, and may include any electromagnetic orultrasonic beam, and even a high pressure fluid jet.

Although a robot is shown for moving the laser beam, any method ofmoving the beam relative to the part is considered within the teachingsof this invention. As examples, the beam could be moved by movingmirrors, as is well-known in laser technology, or could be guided onrails.

A preferred embodiment of the present invention has been disclosed,however, a worker of ordinary skill in the art would recognize thatcertain modifications would come within the scope of this invention. Forthat reason the following claims should be studied in order to determinethe true scope and content of the present invention.

I claim:
 1. A method of machining a workpiece comprising the stepsof:(i) directing a laser beam onto a workpiece and continuously movingthe laser beam along a workpiece surface to etch a first path into theworkpiece surface; (ii) cutting material away from the workpiece along asecond path, with a second path intersecting the first path to thedefine break points for chips of removed material; and (iii) whereinsaid the first path defines a continuing pattern on the workpiece, andthe second path sequentially intersects several points on the firstpath, the distance between subsequent intersection points defining thelength of a chip that is removed from the workpiece, the pattern beingselected such that the maximum chip length is less than a desiredmaximum.
 2. A method of machining a workpiece as recited in claim 1,wherein the laser beam is mounted on a moving member, and the laser beamis moved by moving said moving member.
 3. A method of machining aworkpiece comprising the steps of:(i) directing a fluent beam onto aworkpiece, and continuously moving the fluent beam along a workpiecesurface to etch a first path into the workpiece surface; (ii) cuttingmaterial away from the workpiece along a second path, with the secondpath intersecting the first path to define break points for chips ofremoved material; and (iii) wherein the first path defines a continuingpattern on the workpiece, and the second path sequentially intersectsseveral points on the first path, the distance between subsequentintersection points defining the length of a chip that is removed fromthe workpiece, the pattern being selected such that the maximum chiplength is less than the desired maximum.
 4. A method is recited in claim3, wherein said fluent beam is a laser beam.